1. Field of the Invention
The present invention relates to a brushless motor.
2. Description of the Related Art
So-called outer-rotor brushless motors, in which a rotor magnet is arranged radially outward of a stator, are often used as a main motor for an office automation appliance, a motor for a blower, and the like.
The brushless motors of this type are required to perform reliably even under severe conditions. The main motor of an office automation appliance, for example, is often used for a long time under a high temperature environment. Therefore, the brushless motors of this type are required to withstand a heat shock test. In addition, the brushless motors of this type are required to have high reliability in load-carrying capacity and impact resistance. Use of large-diameter bearings is desirable for the brushless motors to achieve the aforementioned characteristics. Moreover, it is necessary to join components of the brushless motor to one another securely in order to prevent an application of an external force to the brushless motor from causing detachment of any component from the brushless motor.
For the above-described reasons, it is desirable to join the components to one another securely by a structural method, such as swaging or screwing, rather than through adhesion or other less robust securing methods.
Meanwhile, miniaturization of devices in which the brushless motors are installed requires a reduction in the size of the brushless motors as a whole.
The outside diameter of the brushless motor is influenced by the radial dimension of a rotor hub, the radial dimension of a rotor magnet, the radial dimension of teeth of a stator core, the radial dimension of a core back portion of the stator core, the radial dimension of a housing, and the outside diameter of bearings. Notice here that magnetic properties of the brushless motor will deteriorate if the radial dimension of the rotor hub, the radial dimension of the rotor magnet, and the radial dimension of the teeth of the stator core are decreased to reduce the diameter of the brushless motor.